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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4><a name = "tag_000_007_1387">&nbsp;</a>NAME</h4><blockquote>
pthread_key_create - thread-specific data key creation
</blockquote><h4><a name = "tag_000_007_1388">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="pthread.h.html">pthread.h</a>&gt;

int pthread_key_create(pthread_key_t *<i>key</i>, void (*<i>destructor</i>)(void*));
</code>
</pre>
</blockquote><h4><a name = "tag_000_007_1389">&nbsp;</a>DESCRIPTION</h4><blockquote>
This function creates a thread-specific data
key visible to all threads in the process.
Key values provided by
<i>pthread_key_create()</i>
are opaque objects used to locate thread-specific data.
Although the same key value may be used by different threads,
the values bound to the key by
<i><a href="pthread_setspecific.html">pthread_setspecific()</a></i>
are maintained on a per-thread basis and persist
for the life of the calling thread.
<p>
Upon key creation,
the value NULL is associated with the new key in all active threads.
Upon thread creation,
the value NULL is associated with all defined keys in the new thread.
<p>
An optional destructor function may be associated with
each key value.
At thread exit, if a key value has a non-NULL destructor pointer,
and the thread has a non-NULL value associated with that key,
the function pointed to is called with the current associated value
as its sole argument.
The order of destructor calls is unspecified
if more than one destructor exists for a thread when it exits.
<p>
If, after all the destructors have been called for all non-NULL values
with associated destructors,
there are still some non-NULL values with associated destructors,
then the process will be repeated.
If, after at least PTHREAD_DESTRUCTOR_ITERATIONS
iterations of destructor calls for outstanding non-NULL values,
there are still some non-NULL values with associated destructors,
implementations may stop calling destructors,
or they may continue calling destructors
until no non-NULL values with associated destructors exist,
even though this might result in an infinite loop.
</blockquote><h4><a name = "tag_000_007_1390">&nbsp;</a>RETURN VALUE</h4><blockquote>
If successful, the
<i>pthread_key_create()</i>
function stores the newly created key value at
<i>*key</i>
and returns zero.
Otherwise, an error number is returned to indicate the error.
</blockquote><h4><a name = "tag_000_007_1391">&nbsp;</a>ERRORS</h4><blockquote>
The 
<i>pthread_key_create()</i>
function will fail if:
<dl compact>

<dt>[EAGAIN]<dd>
The system lacked the necessary resources to create another thread-specific
data key, or the system-imposed limit on the total number of keys per process
PTHREAD_KEYS_MAX has been exceeded.

<dt>[ENOMEM]<dd>
Insufficient memory exists to create the key.

</dl>
<p>
The
<i>pthread_key_create()</i>
function will not return an error code of [EINTR].
</blockquote><h4><a name = "tag_000_007_1392">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_1393">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_1394">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_1395">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="pthread_getspecific.html">pthread_getspecific()</a></i>,
<i><a href="pthread_setspecific.html">pthread_setspecific()</a></i>,
<i><a href="pthread_key_delete.html">pthread_key_delete()</a></i>,
<i><a href="pthread.h.html">&lt;pthread.h&gt;</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from the POSIX Threads Extension (1003.1c-1995)
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Copyright &copy; 1997 The Open Group
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